1. Field of the Invention
The present invention relates to a printed circuit board (hereinafter, simply referred to as PCB) design support system, a PCB design method and a storage medium storing a control program for a same and more particularly to the PCB design support system and PCB design method to reduce emission of unwanted electromagnetic waves caused by variations in voltages between a power plane and a ground plane on a multilayer PCB by controlling voltage variations, and an equivalent circuit model expressed by an equivalent circuit to implement the above system and method.
2. Description of the Related Art
A PCB is generally composed of electronic parts or elements such as ICs (Integrated Circuits), LSIs (Large Scale Integrated Circuits) or a like and of wirings used to connect these electronic parts or elements and is mounted on almost all electronic devices as their core portions. When an electronic circuit on a PCB is operated, a voltage is generated and a current flows, causing an electromagnetic wave to be emitted. As high-speed processing of signals becomes widespread, higher frequencies are increasingly used for circuit operations, which causes emission of unwanted electromagnetic waves in electronic devices, thus creating problems associated with electromagnetic interference in wireless communications, radio, TV or a like in environments surrounding such electronic devices. Therefore, VCCI (Voluntary Control Council for Interference by Information Technology Equipment in Japan) obliges manufacturers of electronic devices to reduce emission of unwanted electromagnetic waves from electronic devices to a controlled level or less.
It is well known that, in a multilayer PCB, a ground plane to provide a reference potential in circuits and a power plane to provide operating power to ICs and/or LSIs are, generally, of a plane structure and the ground plane and power plane function as parallel-plate lines and that variations in voltages between the power plane and ground plane causes emission of unwanted electromagnetic waves (refer to Transaction of the Institute of Electronics, Information and Communication Engineers, Vols. E-80-B, No.11, November 1997, p. 1645-1651). To reduce the emission of unwanted electromagnetic waves caused by variations in voltages between the power plane and ground plane, PCBs having various kinds of structures are introduced and various kinds of methods for designing the PCB are available accordingly.
One example of conventional technology is disclosed in Japanese Patent Application Laid-open No. Hei 11-145569 entitled xe2x80x9cPrinted Circuit Board and Method for Designing Samexe2x80x9d, in which, as shown in FIGS. 30A and 30B, a plurality of conductive patterns 102a and signal lines 105a both extending in a direction of length of a base material 101 are formed on a part-mounting surface of a rectangular and plate-like, base material 101. On a soldering surface disposed opposite to the part-mounting surface of the base material 101 is formed a plurality of conductive patterns 102b and signal lines 105b extending in a direction perpendicular to the direction of the length of the base material 101 as shown in FIG. 30B. The conductive patterns 102a and 102b are used as a power pattern or a ground pattern. Moreover, separated parts of the conductive patterns 102a and 102b are connected to each other via a chip-type resistor 104. By using this chip-type resistor 104, a decrease in impedance of the conductive patterns 102a and 102b occurring at a frequency of a standing wave generated from a relationship between a size of the base material 101 and a wavelength of radiation noise is suppressed by loss factor induced by the chip-type resistor 104, thus resulting in a decrease of a Q value (resonance frequency) in resonance of the standing wave, leading to reduction of emissions of unwanted electromagnetic waves.
Another example of the conventional technology is disclosed in Japanese Patent Application Laid-open No. Hei 11-40905 entitled xe2x80x9cPrinted Circuit Board and Electronic Devicexe2x80x9d, in which, as shown in FIG. 31, the PCB 110 is composed of a power layer 111, a ground layer 112 and dielectrics 113a and 113b disposed between the power layer 111 and the ground layer 112. There ate mounted two kinds of dielectrics 113a and 113b each having a different dielectric constant and is configured so that their dielectric constants are in a distributed state on plane faces of the power layer 111 and the ground layer 112 to make resonance weak in a widely distributed state on an axis of frequencies by giving a different resonance condition to each point of the plane face, thus achieving reduction in emissions of strong unwanted electromagnetic waves at a specified frequency.
Moreover, another example of the conventional technology is disclosed in Japanese Patent Application Laid-open No. Hei 10-275981 entitledxe2x80x9cMultilayer Printed Circuit Boardxe2x80x9d, in which, as shown in FIG. 32, capacitors 124 adapted to cause high frequency current flowing in a power layer 122 to flow into a ground layer 123 are mounted on edge portions of the power layer 122 and of the ground layer 123 in continuous or discrete positions, thereby achieving reduction of emissions of unwanted electromagnetic waves from the multilayer PCB, having a signal layer 121, the power layer 122 and the ground layer 123.
Another example is disclosed in Japanese Patent Application Laid-open No. Hei 6-203102 entitled xe2x80x9cPrinted Circuit Board Wiring Methodxe2x80x9d, in which, as shown in FIG. 33, each of blocks 132, 133, . . . , 143 are disposed on a multilayer PCB 131 in a manner that digital signals containing much higher frequency components can be sent or received in a straight-line manner in an X or Y direction among these blocks. In this method, therefore, by forbidding cut lines 161 and 162 disposed orthogonal to a direction of wirings to allow digital signals containing much higher frequency components to flow in regions overlapping other regions 151, 152 or 153 disposed adjacent respectively to a layer having wirings to allow digital signals containing much higher frequency components to flow among blocks mounted on a power layer and a ground layer (not shown), overlap each other, emissions of unwanted electromagnetic waves are reduced.
Furthermore, another example disclosed in the Japanese Patent Application Laid-open No. Hei 10-97560 entitled xe2x80x9cComputer Aided Design Systemxe2x80x9d, in which, as shown in FIG. 34, by using a tool 171 for evaluation on an arrangement of a bypass condenser incorporated in the CAD (Computer Aided Design) system, parameters associated with a wiring path of the bypass condenser is determined based on information obtained through a substrate data device 174 required for layout of a PCB and then, based on an impedance characteristic calculated from determined parameters, a range of effectiveness that can be provided by the bypass condenser is determined. Parameters associated with the wiring path of the bypass condenser include a wiring length, resistivity, wiring width, wiring thickness or a like. The above tool 171 has a function to display determined range of effectiveness provided by the bypass condenser, which is approximated by an ellipse, on a display device 175. The CAD system, by using this function, designs the PCB in which emissions of unwanted electromagnetic waves are reduced.
However, each of the above examples of conventional technologies has a problem.
In technology disclosed in the Japanese Patent Application Laid-open No. Hei 11-145569 (FIG. 30A and FIG. 30B), though resonance occurring among wirings can be reduced by insertion of the resistor 104, since a voltage drop occurs due to the insertion of the resistor 104, it is impossible to reduce resonance in power lines. Therefore, the emissions of unwanted electromagnetic waves caused by variations in voltages between the power plane and the ground plane cannot be fully reduced. Moreover, in technology disclosed in the Japanese Patent Application Laid-open No. Hei 11-40905 (FIG. 31) use of two dielectrics, dielectrics 113a and 113b, each having different dielectric constant is required which causes complex structures of the PCB. Also, in technology disclosed in the Japanese Patent Application Laid-open No. Hei 10-275981 (FIG. 32), since a device to be inserted into the edge portion of the substrate is the capacitor 124 being a reactance device, though a resonance frequency between the power layer 111 and ground layer 112 is changed, resonance itself cannot be suppressed. That is, this technology is effective only when radiation of electromagnetic waves is affected by a shift in frequencies. Technology disclosed in the Japanese Patent Application Laid-open No. Hei 6-203102 (FIG. 33) is featured by having no discontinuous portion in a path for return currents in a signal wiring system. Therefore, though the emissions of unwanted electromagnetic waves from signal wiring system can be reduced, it is difficult to suppress the unwanted electromagnetic waves caused by variations in voltages between the power plane and ground plane. Furthermore, technology disclosed in the Japanese Patent Application Laid-open No. Hei 10-97560 (FIG. 34) is one which is required for determining the wiring path of the bypass condenser and which is effective in reducing variations in voltages between the power plane and ground plane caused by switching noise occurring in active elements such as LSIs, ICs or the like, however, it is not effective in reducing variations in voltages caused by an interlayer via-hole used to connect signal lines mounted between different layers and by coupled signal lines mounted in a layer put between the power plane and ground plane.
In order to shorten a development timescale for electronic devices on which the PCB is mounted, there is a strong demand for incorporating a measure to reduce emissions of unwanted electromagnetic waves from the PCB, in a precautionary manner, from a starting stage of designing the PCB. Moreover, to reduce costs of the PCB, a method for the reduction of the emissions of unwanted electromagnetic waves from the PCB by optimizing layout of the PCB while following conventional designing and circuit-arranging methods without using additional new parts or employing new specific wiring structures leading to increased costs, is needed.
In view of the above, it is an object of the present invention to provide a PCB design support system, a PCB design method capable of reducing radiation of electromagnetic waves by optimizing layout of a substrate while following a conventional method for designing the PCB and maintaining a conventional structure, and a storage medium storing a control program for a same.
According to a first aspect of the present invention, there is provided a PCB design support system including:
an inputting means to input information about ground plane structure, power plane structure and layout of a PCB including information about positions of mounting active elements such as LSIs, ICs or a like and at least one decoupling capacitor;
a section to build a circuit model expressed by an equivalent circuit for calculating, using the input information, voltage distribution between the ground plane and the power plane;
a section to select a specified frequency and to calculate voltage distribution occurring at the specified frequency between the ground plane and the power plane;
a section to display the calculated voltage distribution in a form of a two-dimensional voltage distribution map in a manner to correspond to a shape of the PCB; and
a section to store results obtained from the above operations.
In the foregoing, a preferable mode is one wherein the section to display the voltage distribution puts the voltage distribution map on the PCB in a manner that they overlap each other and displays regions expressing voltage levels on the voltage distribution map in order of decreasing voltage strength and in stages.
Also, a preferable mode is one that wherein includes a section to partition regions of the voltage distribution map in order of decreasing voltage strength and in stages to classify the partitioned regions on the voltage distribution map into regions specified in stages in accordance voltage levels including one region where disposing of a via-hole straddling the ground plane and the power plane is prohibited and one region where disposing of the via-hole is allowed.
Also, a preferable mode is one wherein the section to calculate the voltage distribution calculates, instead of the voltage distribution, complex impedance between the ground plane and the power plane and displays absolute values of results of calculation.
Also, a preferable mode is one that wherein includes a section to extract a position of the via-hole straddling the ground plane and the power plane based on input information about signal wiring including layout information, a section to set the extracted position of the via-hole to the voltage distribution map of the calculated voltage distribution occurring between the ground plane and the power plane and/or to display the extracted position of the via-hole on the voltage distribution map and a section to issue a sign that gives warning to any said via-hole disposed in a region where a voltage is at a high level.
Also, a preferable mode is one that wherein includes a section to provide an instruction that a capacitor to connect the ground plane to the power plane is mounted near the via-hole formed so as to straddle the ground plane and the power plane and mounted in a region where a voltage is high.
Also, a preferable mode is one that wherein includes a section to find out and specify a region having a lower voltage to which any via-hole given the sign that gives warning is able to be moved and/or to instruct the PCB design support system to automatically move the via-hole given the sign that gives warning to the low-voltage region.
According to a second aspect of the present invention, there is provided a method of designing a PCB including steps of:
an inputting means to input information;
inputting information about ground plane structure, power plane structure and layout of a PCB including information about positions of mounting active elements such as LSIs, ICs or a like and at least one decoupling capacitor;
building a circuit model expressed by an equivalent circuit, using input information, to calculate voltage distribution between the ground and the power plane;
selecting a specified frequency and calculating voltage distribution occurring at the specified frequency between the ground plane and the power plane;
displaying obtained voltage distribution in a form of a two-dimensional voltage distribution map in a manner to correspond to a shape of the PCB; and
deciding, using the voltage distribution map, a position of disposing a via-hole for signal wiring which straddles the ground plane and the power plane.
According to a third aspect of the present invention, there is provided a PCB support system including:
a section to input information about ground plane structure, power plane structure and layout of a PCB including information about positions of mounting active elements such as LSIs, ICs or a like and at least one decoupling capacitor;
a section to build a circuit model for calculating, using the input information, distribution of currents flowing on both the ground plane and the power plane;
a section to select a specified frequency and to calculate distribution of currents flowing, at the specified frequency, in two directions in a manner being parallel to ends of the ground plane and the power plane, on both the ground plane and the power plane;
a section to display separately each of the current distributions obtained in the two current flowing directions in a form of a two-dimensional current distribution map in a manner to correspond to a shape of the PCB; and
a section to store results obtained from operations.
In the foregoing, a preferable mode is one wherein the section to display the current distribution puts the current distribution map on the PCB in a manner that they overlap each other and displays regions expressing current levels on the current distribution map in order of decreasing current strength and in stages, separately for each of current distributions obtained in the two current flowing directions.
Also, a preferable mode is one that wherein includes a section to partition regions of each of the current distribution maps obtained in the two current flowing directions in order of decreasing current strength and in stages to classify the partitioned regions on the current distribution map into regions specified in stages in accordance current levels including one region where installation of wiring in a same direction as for current flowing direction in a layer disposed between the ground plane and the power plane is prohibited and one region where the installation of wiring is allowed.
Also, a preferable mode is one that wherein includes a section to extract a position of the wiring installed in the layer disposed between the ground plane and the power plane based on input information about signal wiring including layout information, a section to set the extracted position of the wiring installed in the layer to each of the current distribution maps of the calculated current distributions obtained in the two current flowing directions between the ground plane and the power plane and/or to display the extracted position of the wiring on the current distribution map and a section to issue a sign that gives warning to any wiring installed in the same direction as for current flowing direction in the layer disposed between the ground plane and the power plane and disposed in a region where a current is at a high level.
Also, a preferable mode is one that wherein includes a section to find out and specify a region where the current flowing on both ground plane and the power plane is at a low level, to which the wiring given the sign that gives warning is able to be moved for installation and/or to instruct the PCB design support system to automatically move the wiring given the sign that gives warning to the low-current region.
According to a fourth aspect of the present invention, there is provided a method of designing a PCB including steps of:
inputting information about ground plane structure, power plane structure and layout of a PCB including information about positions of mounting active elements such as LSIs, ICs or a like and at least one decoupling capacitor; building a circuit model for calculating, using input information, currents flowing on both the ground plane and the power plane;
selecting a specified frequency and calculating distribution of current flowing in two directions in a manner being parallel to ends of the ground plane and power plane, at the specified frequency, on both the ground plane and the power plane;
displaying separately each of current distributions obtained in the two current flowing directions in a form of a two-dimensional current distribution map in a manner to correspond to a shape of the PCB; and
deciding, using a current distribution map, a position of installing wiring in a layer put between the ground plane and the power plane.
Also, according to a fifth aspect of the present invention, there is provided a machine-readable storage medium storing a control program used for designing a PCB, wherein the control program causes a computer to carry out steps of:
inputting information about ground plane structure, power plane structure and layout, of a PCB including information about positions of mounting active elements such as LSIs, ICs or a like and at least one decoupling capacitor, building a circuit model for calculating, using input information, voltage distribution between the ground plane and the power plane, selecting a specified frequency and of calculating voltage distribution occurring at the specified frequency between the ground plane and the power plane, displaying obtained voltage distribution in a form of a two-dimensional voltage distribution map in a manner to correspond to a shape of the PCB, and deciding, using the voltage distribution map, a position of disposing a via-hole formed in a manner to straddle the ground plane and the power plane.
Also, according to a sixth aspect of the present invention, there is provided a machine-readable storage medium storing a control program used for designing a PCB, wherein the control program causes a computer to carry out steps of:
inputting information about ground plane structure, power plane structure and layout of a PCB including information about positions of mounting active elements such as LSIs, ICs or a like and at least one decoupling capacitor, building a circuit model for calculating, using the input information, distribution of currents flowing on both the ground plane and the power plane, a step of selecting a specified frequency and calculating distribution of currents flowing, at the specified frequency, in two directions in a manner being parallel to ends of the ground plane and the power plane, on both the ground plane and the power plane, displaying separately obtained two current distributions obtained in two current flowing directions in a form of a two-dimensional current distribution map in a manner to correspond to a shape of the PCB, and deciding, by using the current distribution map, a position of installing wiring in a layer put between the ground plane and the power plane.
According to a seventh aspect of the present invention, there is provided a equivalent circuit model expressed by an equivalent circuit for supporting design of a PCB to calculate distribution of voltages between a ground plane and a power plane, distribution of currents flowing on the ground plane and the power plane and complex impedance between the ground plane and the power plane including an equivalent circuit in which both the ground plane and the power plane are expressed by a capacitor, an inductor and a resistor and the resistor is connected in parallel to the capacitor to express dielectric loss by a dielectric contained in the PCB.
In the foregoing, it is preferable that a resistor is connected to ends of the equivalent circuit to express radiation loss caused by an emission of electromagnetic wave.
According to an eighth aspect of the present invention, there is provided a PCB design support system provided with a control program for designing a PCB, wherein the control program causes a computer to carry out steps of:
inputting information about ground plane structure, power plane structure and layout of a PCB including information about positions of mounting active elements and at least one decoupling capacitor;
building a circuit model for calculating, using input the information, voltage distribution between the ground plane and the power plane;
selecting a specified frequency and of calculating voltage distribution occurring at the specified frequency between the ground plane and the power plane;
displaying the obtained voltage distribution in a form of a two-dimensional voltage distribution map in a manner to correspond to a shape of the PCB; and
deciding, using the voltage distribution map, a position of disposing a via-hole formed in a manner to straddle the ground plane and the power plane.
According to a ninth aspect of the present invention, there is provided a PCB design support system provided with a a control program for designing a PCB, wherein the control program causes a computer to carry out steps of:
inputting information about ground plane structure, power plane structure and layout of a PCB including information about positions of mounting active elements such as LSIs, ICs or a like and at least one decoupling capacitor;
building a circuit model for calculating, using input the information, distribution of currents flowing on both the ground plane and the power plane;
selecting a specified frequency and calculating distribution of currents flowing, at the specified frequency, in two directions in a manner being parallel to ends of the ground plane and the power plane, on both the ground plane and the power plane;
displaying separately the obtained two current distributions obtained in the two current flowing directions in a form of a two-dimensional current distribution map in a manner to correspond to a shape of the PCB; and
deciding, by using the current distribution map, a position of installing wiring in a layer disposed between the ground plane and the power plane.